Automatic recirculating control for pumps



April 15, 1952 H. A. SCHLlEDER AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Filed April 19, 1949 TO RESERVOIR INTAKE 5 Sheets-Sheet 1 FIG.

JNVENTOR. HAROLD A. SCHLIEDER HTTOR/VEY April 15, 1952 H. A. SCHLIEDER 2,593,053

AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Filed April 19, 1949 3 Sheets-Sheet 2 FIG. 2

INVENTOR. HAROLD A.5CHLIEDER "Maw AT TORNE Y April 15, 1952 H. A. SCHLIEDER AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Filed April 19, 1949 3 Sheets-Sheet 3 FIG. 5

INVENTOR. HAROLD A. SCHLIEDER Patented Apr. 15, 1952 AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Harold Augustus Schlieder, Syracuse, N. Y., as-

signor to Continental Foundry and Machine Company, East Chicago, 1nd,, a corporation of Delaware Application April 19, 1949, Serial No. 88,394

7 Claims.

This invention relates to an automatic recirculating control device for centrifugal type boiler feed pumps driven at a substantially constant speed, and more particularly to a control device of this type adapted to be directly operated by use of the pump power.

It is well known that at periods of relatively low or no load on centrifugal type feed water pumps for boilers, serious damage to the pump may occur if the feed water control valve disposed between the pump and the boiler is substantially closed. This is due to the fact that the water delivered to the pump for boiler feeding is only a few degrees below the critical temperatures for the pressure and if it cannot pass through the pump immediately it may flash into steam, due to the heat units imparted thereto by the pump impeller. Then the boiler cannot receive feed water even though in response to boiler demand the valve in the pump discharge line has opened wide.

In my co-pending application Serial No. 42,873, filed August 6, 1948, an arrangement was disclosed wherein a boiler feed water pump driven by a steam turbine could have feed water automatically recirculated through the pump in response to load conditions on the turbine where by at light load demands on the pump feed water is recirculated therethrough in accordance with a predetermined minimum pressured drop through the turbine.

The present invention relates to pumps of the above type wherein a steam turbine is not available for controlling recirculation of feed water through the pump and means independent of the pump driving means must be employed to effect automatic recirculation of feed water through the pump under light demands for feed water.

I am aware that it has previously been proposed in a boiler feed water system to provide a recirculating line having flow therethrough controlled by a fluid pressure motor operated valve, the motor being loaded from an air pressure line through a pilot valve responsive to a given condition in a flow meter disposed in the feed water system. Also, I am aware that in similar systems employing an air pressure line a switch responsive to a given condition in a flowmeter disposed in the boiler feed water system is used to energize a solenoid valve in the air line. However, I am not aware that it has previously been proposed to directly utilize the fluid being- ,Water pump driven by a substantially constant speed motor has means intermediate the discharge side of the pump and the boiler which will automatically cause recirculation of feed water through the pump when the demand for boiler feed water drops below a pre-determined value. A fluid flow measuring device connected across an orifice in the pump discharge line is adapted at a pre-determined minimum flow in the discharge line, to actuate means utilizing the pump power to cause the pump recirculating valve to open.

It is a primary object of the invention to provide improved means for automatic recirculation of boiler feed water through a substantially constant speed pump in response to a pre-determined minimum flow at the discharge side of the pump.

Another object of the invention is to provide means in a boiler feed water system for automatically preventing damage to a boiler feed water pump driven by a substantialy constant speed motor.

Another object of the invention is to provide in a boiler feed water system relatively simple means directly using feed water being pumped, for automatically causing recirculating flow through a boiler feed water pump driven by a substantially constant speed motor when the boiler demand for feed water reaches a predetermined minimum.

Other objects of the invention and the invention itself will be increasingly understood from a consideration of the following description and drawings wherein:

Fig. 1 is a View, largely diagrammatic, of a boiler feed water system embodying my invention;

Fig. 2 is a top plan view of the recirculating valve illustrated in Fig. 1;

Fig. 3 is a section taken along the line 33 of Fig. 2;

Fig. 4 is an enlarged elevational view of a preferred type of differential pressure responsive device I may employ;

Fig. 5 is a section taken along line 55 of Fig. 4; and

Fig. 6 is a vertical sectional taken through the pilot valve oi the device or along the line 6-4 of Fig. 4.

Referring now to the drawings, and particularly Fig. l, I have illustrated at It a conventional substantially constant speed motor having a driven shaft II which is connected to a shaft I2 of a pump i3 by a coupling M. The pump is of the multistage type and is adapted to receive boiler feed water from an inlet conduit [3 and discharge the same through an outlet conduit ii.

It will be readily appreciated that if the boiler feed water control valve (not shown) and dis posed in the conduit i1 between the pump I3 and the boiler (not shown) is substantially closed in accordance with light or negligible demands on the boiler that it is highly undesirable to have water transmitted to the pump converted into steam due to heat units imparted thereto while confined in the pump. The arrangement for causing boiler feed water under these conditions to be forced back into the pump supply system and preferably to the pump storage tank will now be explained. The pump discharge conduit I! has an orifice or reduced'diameter passage therein at a location such as indicated at 18 whereby in a well known manner a pressure differential will be created on the upstream and downstream sides of the orifice in accordance with fluid flow. A differential pressure responsive device generally indicated at E9 has a fluid conduit 21 from the downstream side of the orifice and a conduit 22 from the upstream side of the orifice extending thereto.

The differential pressure responsive device, best illustrated in Figs. 1 and 5, comprises an upper housing 23 and a lower housing 24 sealingly gripping a rubber or the like flexible diaphragm 26 therebetween to form an upper chamber 21 and a lower chamber 28. The downstream or high pressure side of the orifice communicates with chamber 21, and the upstream or low pressure side communicates with the chamber 28.

It will now be apparent that the diaphragm 25 will be moved by differential fluid pressure in the chambers 27 and 28. Downward movement of the diaphragm is resisted by a compression spring 23 adjustable by a threaded element 3| engaging a screw 35. Element 3! can move axially but is prevented from rotating in any suitable manner as by providing upstanding fingers (not shown) on the base of housing 24 slidably engaging slots in element 3| whereby as screw 35 is rotated element 3| will be moved axially to vary the force exerted by spring 29. A stem 32 movable by the diaphragm actuates a rock arm 33 fixed to a shaft 34 extending externally of housing 23 through a fluid seal. Shaft 34 has a lever arm 36 fixed thereto externally of device l9 to which is adjustably pivoted a link 31. The lower end of link 31 is adjustably pivoted to a second lever 38 fixed to the plug of a pilot valve 40. It will now be apparent, that when the fluid pressure in chamber 21 drops to a point relative to the fluid pressure in chamber 28 enabling the pressure in chamber 28 with the assistance of adjustable spring 23 tomove diaphragm 26 upwardly, the lever 36 will be rocked in a counterclockwise direction and lever 38 will be rocked in a clockwise direction (Fig. This will occur when the fluid flow through pump discharge conduit H or the pressure differential across the restricted orifice located at 18 drops to a predetermined value.

Pilot valve 40, as best illustrated in Fig.6, is of conventional type wherein a port M in the plug thereof is adapted to selectively effect com munication between a diaphragm valve port 42 and a supply port 43 or an exhaust port 44 or cut off communication between port 42 and both ports 43 and 44. Port 42 is connected through a line 46 with a chamber 41 of a recirculating flow control valve generally indicated at 48. One wall of chamber 41 is formed by a flexible rubber or the like diaphragm 49, the other side of the diaphragm being subjected to atmospheric pressure by providing suitable ports as indicated at 50. Secured to diaphragm 49 is a valve stem 5! and downward movement of the daphragm is resisted by an adjustably mounted compression spring 53. Valve port 52 controls fluid flow from an inlet 54 to an outlet 56. Inlet 54 communicates with the pump discharge line I! by a conduit 55 and outlet 56 communicates with the pump suction or inlet line !6 through the system supplying the Jump such as a storage tank or the like by a :onduit 51 leading to the storage tank or reservoir intake. The port 43 of the pilot valve communicates by a conduit 25 with a relatively high pressure zone of the pump [3 whereas the pilot valve port 44 communicates with a relatively low pressure zone of the pump by a conduit 30-.

The operation of the apparatus described will now be explained. The pump l3 will be driven at a substantially constant speed by the motor l0 despite varying demands of the boiler as to feed water. First, assume there is a relatively heavy demand by the boiler for feed water. Feed water will be discharged from the pump at a rate sufiicient to create considerable pressure differential at l8 due to the restricted orifice. This pressure differential communicated to the device IE will hold or place the pilot valve in a position whereby supply port 43 from a high pressure zone of the pump will communicate with port 42 to transmit said pressure to diaphragm 49 of the recirculating control valve to maintain valve port 52 therein closed. This means that all feed water discharged from the pump will pass to the boiler.

Second, assume that the boiler feed water con trol valve demands a negligible amount of feed water. The rate of fluid flow through the orifice located at I8 will be negligible and the pressure different at opposite sides of the orifice will be resultantly negligible. Reduction in fluid pressure in chamber 2'! of device l9 will permit spring 29 to actuate the pilot valve whereby port 42 will be placed in communication with port 44 so that fluid pressure on diaphragm 49 of the recirculating control valve will be reduced through exhaustion of fluid to one of the lower stages of the pump and port 52 will be uncovered permitting recirculating flow through the pump and the portion of its supply system included in the recirculating circuit.

When the boiler feed water control valve in response to demands on the boiler opens to a degree that the flow through the pump discharge line causes a pre-determined pressure differential across the orifice the diaphragm 26 will be moved downwardly and cause rotation of the pilot valve plug 4| to a position effecting communication between ports 42 and 43. Port 43 a com municates with a relatively high pressure stage of the pump I3 and this pressure exerted on diaphragm 47 of valve 48 closes port 52 and stops recirculating flow.

Adjustment of spring 29 will determine the value of which the pressure differential across the orifice or the flow through pump discharge line will drop before recirculating flow is started. Spring 53 of valve 49 can be adjusted to conform with the relatively high and low pressures available at the pump so that high pressure on diaphragm 4'! will overcome the spring and the spring will overcome the low pressure.

It will now be apparent that I have provided automatic means for initiating recirculating flow from a pump discharge line through a circuit including the pump when flow through the discharge line reaches a predetermined minimum. Also, considerable power is available for operating the recirculating control since pump pressure is used. Although the invention has particular application to a boiler feed water system and has been described in connection with such a system, it will be apparent that it is adaptable to any system wherein it is desired to prevent damage to a pump or suction loss when discharge flow is reduced to a point which might cause these undesirable pump conditions.

I preferably locate the restricted orifice or flow measuring means beyond the recirculating discharge line, as indicated at 13, where only flow to the boiler is measured. However, the orifice can be located ahead of the recirculating line but in that case it would measure the quantity of fluid being recirculated and require a tripper type or intermittent acting valve.

Although I have illustrated a multi-stage pump it is understood that a single stage pump could be used and in this embodiment the pilot valve supply connection would be taken from the pump discharge line and the pilot valve return line would extend to a drain.

I have illustrated at 58 a by-pass connection extending between chambers 21 and 28 of device I9 which is in effect an equalizing line used to place the unit in service. The by-pass valve is opened before starting to equalize the pressure on both sides of diaphragm 26 and thereby preventing the diaphragm from being subject to full pressure on only one side thereof.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, since obvious modifications will occur to persons skilled in the art.

What I claim is as follows:

1. The combination with a unit comprising a pump, a liquid supply system for the pump, a liquid discharge line extending from the pump and adapted to have flow therethrough substantially varied, and a substantially constant speed motor for driving the pump, of means for automatically recirculating liquid through the pump when flow through the discharge line drops to a pre-determined value, said means comprising a liquid conduit extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in the conduit, means in the discharge line for creating pressure differential in accordance with liquid flow through the line, and means under control of the pressure differential means for operating said valve by the pump power when flow through the discharge line reaches a pre-determlned value.

2. The combination as described in claim 1 and wherein the valve is operated by a fluid pressure motor, conduit means extended from the pump to the motor, and flow through the conduit means for actuating the motor is controlled by the pressure differential means.

3. The combination as described in claim 1 and wherein a fluid pressure motor is adapted to actuate the valve, conduit means extend from the motor to the pump, a pilot valve controls fluid flow through the conduit means, and the pilot valve is actuated by the pressure differential means.

4. The combination with a unit comprising a multi-stage pump, a liquid supply system for the pump, a liquid discharge line extending from the pump adapted to have flow therethrough substantially varied, and a substantially constant speed motor for driving the pump, of means or automatically recirculating liquid through the pump when flow through the discharge line reaches a pre-determined low value, said means comprising a liquid conduit extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in the conduit, means in the discharge line for creating pressure differential in accordance with liquid flow through the line, a fluid pressure motor for actuating the valve, a pilot valve communicating with the motor, connections extending from the pilot valve to high and low pressure stages of the pump, and the pilot valve being controllable by the pressure differential means whereby when the pressure differential in the pump discharge line reaches a pre-determined low value communication will be effected between a relatively low pressure stage of the pump and the motor permitting the valve to open and when the pressure differential reaches a predetermined high value communication will be effected between a relatively high pressure stage of the pump and the motor causing the valve to close.

5. The combination as described in claim 4 and wherein the pilot valve is adjustable whereby it may be actuated at different pressure differentials in the discharge line.

6. The combination as described in claim 4 and wherein the fluid pressure motor is adjustable whereby it may move the valve toopen and closed position under different pressure at the relatively high and low stage connections with the pump.

7. The combination with a boiler feed water system of the type including a feed water pump adapted to be driven at a substantially constant speed, a discharge line extending from the pump to a feed water control valve, and a recirculating line extending from the discharge line to a point in the pump supply system, of means for automatically causing flow through the recirculating line when flow through the discharge line reaches a pre-determined low value, said means comprising a valve in the recirculating line, means in the discharge line ahead of the connection between the discharge and recirculating lines for creating pressure differential in accordance with liquid flow through the discharge line, a fluid pressure motor for operating the recirculating line valve, a pilot valve communicating with the pressure differential means adapted to be actuated at a pre-determined minimum pressure differential, conduit means adapted to communicate pump power to the motor, and the pilot valve controlling flow through the conduit means whereby the recirculating line valve will be opened at said minimum pressure differential.

HAROLD AUGUSTUS SCI-ILIEDER.

REFERENCES CITED UNITED STATES PATENTS Name Date Trisler Mar. 8, 1949 Number 

